Traditional fabrics have, for centuries, been decorated and had their surface texture modified by embroidery and other needle arts. Originally, this process was obtained through tedious hand labor, painstakingly applying fine stitches that had the cumulative effect of building up a region of the background fabric according to some particular pattern. The resulting product had a base fabric, comprised of threads or yarns, woven or knitted according to some pattern, a raised region formed by a collection of threads in some stitch pattern, and an overall pattern of these raised regions determined by their respective size, shape, orientation and placement. While rich in appearance, these products were complicated to create and costly to produce.
Most nonwoven fabrics are flat and visually uninteresting. In some instances, nonwoven fabrics are embossed or printed with some sort of design to provide visual interest. In other instances, nonwoven fabrics are provided with an integral pattern during the course of their manufacture. Those having an integral pattern of their own fall into two categories:
1) Apertured fabricsxe2x80x94where a pattern is created by a network of bundled fiber segments surrounding apertures or holes; or
2) Weight patterned fabricsxe2x80x94fabrics that achieve a visual effect by concentrating fibers into regions of higher basis weight to increase opacity relative to the lower basis weight regions which are more translucent.
It is important to differentiate between basis weight and density. xe2x80x9cBasis weightxe2x80x9d is the weight of a unit area of fibrous web or fabric or portion thereof being characterized. Basis weight has also been called xe2x80x9carea densityxe2x80x9d in some prior art patents. The term xe2x80x9cdensityxe2x80x9d is the weight of a unit volume of a fibrous web or fabric or portion thereof being characterized. xe2x80x9cDensityxe2x80x9d has also been called xe2x80x9cvolume densityxe2x80x9d in some prior art patents. Typical embossing processes create regions of higher density without altering the basis weight. Traditional nonwoven patterning processes produce regions of varying basis weight, while maintaining substantially uniform density.
The prior art nonwoven fabrics made with these known patterning processes do not have clear, well defined raised portions and therefore the desired patterns are difficult to see. In addition, the raised portions of prior art embossed nonwoven fabrics are not dimensionally stable and their raised portions lose their three-dimensional structure when stressed, as for example, when they are handled or laundered.
Processes for making nonwoven fabrics have been known for many years. In one process, a fiber batt or web is treated with water streams to cause the fiber to entangle with each other and provide some strength in the batt. Many methods have been developed for treating fiber batts in this manner in an attempt to duplicate the physical properties and appearance of woven fabrics.
U.S. Pat. Nos. 5,098,764 and 5,244,711 disclose the use of a support member in one such method of producing nonwoven fabrics. The support members have a topographical feature configuration as well as an array of apertures. In this process, a starting web of fiber is positioned on the topographical support member. The support member with the fibrous web thereon is passed under jets of high pressure fluid, typically water. The jets of water cause the fiber to intertwine and interentangle with each other in a particular pattern, based on the topographical configuration of the support member.
The pattern of topographical features and apertures in the support member is critical to the structure of the resulting nonwoven fabric. In addition, the support member must have sufficient structural integrity and strength to support a fibrous web while fluid jets rearrange the fibers and entangle them in their new arrangement to provide a stable fabric. The support member must not under go any substantial distortion under the force of the fluid jets. Also, the support member must have means for removing the relatively large volumes of entangling fluid so as to prevent xe2x80x9cfloodingxe2x80x9d of the fibrous web, which would interfere with effective entangling. Typically, the support member includes drainage apertures which must be of a sufficiently small size to maintain the integrity of the fibrous web and prevent the loss of fiber through the forming surface. In addition, the support member should be substantially free of burrs, hooks or the like irregularities that could interfere with the removal therefrom of the entangled fabric. At the same time, the support member must be such that fibers of the fibrous web being processed thereon are not washed away under the influence of the fluid jets.
The present invention is directed to topographical support members and methods of making them. These topographical support members can be used to make nonwoven fabrics having a fibrous background portion in one plane thereof and raised fibrous portions in another plane thereof. There may be two types of raised portions. The basis weight of the first type of raised portion is substantially the same as the basis weight of the background portion of the nonwoven fabric. The basis weight of the second type of raised portion is greater than the basis weight of the background portion.
On type of nonwoven fabric which can be made with support members of the present invention comprises a background portion and at least one raised portion. The background portion is located in and defines a first plane of the nonwoven fabric. The raised portion of the nonwoven fabric is located in a second plane which is above and parallel to the first plane. The raised portion is joined to the background portion by a fibrous transition region. In this specific nonwoven fabric, the basis weight of the raised portion is substantially the same as the basis weight of the background portion. The density of the background portion and the density of the raised portion are substantially the same. A raised portion whose basis weight is substantially the same as the basis weight of the background portion is sometimes referred to as an xe2x80x9cintaglioxe2x80x9d portion.
Another type of nonwoven fabric which can be made with support members of the present invention also comprises a background portion and at least one raised portion. As was the case with the first nonwoven fabric, the background portion is located in and defines a first plane of the nonwoven fabric and the raised portion is located in a second plane which is above and parallel to the first plane. As was the case with the first nonwoven fabric, the raised portion is joined to the background portion by a fibrous transition region. In the case of the second type of nonwoven fabric however, the basis weight of the raised portion is greater than the basis weight of the background portion. The density of the raised portion of this second nonwoven fabric is substantially the same as the density of the background portion. A raised portion whose basis weight is greater than the basis weight of the background portion is sometimes referred to as a xe2x80x9cslubxe2x80x9d portion.
Yet another type of nonwoven fabric which can be made with support members of the present invention, comprises a background portion, at least one first raised portion, and at least one second raised portion. As was the case with the first and second nonwovens discussed above, the background portion is located in and defines a first plane of the nonwoven fabric. The first raised portion is located in a plane which is above and parallel to the first plane. Similarly the second raised portion is located in a plane which is above and parallel to the first plane. Each of the first and second raised portions is joined to the background portion by a fibrous transition region. In this third nonwoven fabric, the basis weight of the first raised portion is substantially the same as the basis weight of the background portion, while the basis weight of the second raised portion is greater than the basis weight of the background portion. In other words, in this third type of nonwoven fabric, the nonwoven fabric has one or more first raised portions which are sometimes referred to as xe2x80x9cintaglioxe2x80x9d portions and one or more second raised portions which are sometimes referred to as xe2x80x9cslubxe2x80x9d portions. It is not necessary that the first raised portion and the second raised portion be in the same plane; rather the first raised portion may be in a plane which is above the plane of the background portion and the second raised portion may be in a plane which is above the plane of the first raised portion.
In the process of forming nonwoven fabrics using the topographical support members of the present invention, a web or layer of fibers or a lightly entangled fibrous web is placed on a foraminous forming plate or topographical support member comprising an essentially planar background surface with at least one relatively wide recessed region significantly displaced from the background surface of the forming plate. Typically, the support member comprises a multiplicity of recessed regions, positioned as depressions in some predetermined array, that will form a desired pattern of raised portions on the nonwoven fabric. Fluid forces, in the form of streams of water, are applied to the upper surface of the starting fibrous web or layer of fibers. Initially, these fluid forces xe2x80x9cmoldxe2x80x9d the starting web to the three dimensional support member; as the process of applying fluid forces continues, the fibers are entangled and locked together so as to provide a nonwoven fabric comprising a background portion and one or more raised portions which are permanently positioned with respect to one another.
In an alternative embodiment, the topographical support member has a relatively narrow recessed region displaced from the planar background surface of the forming plate. The present invention is directed to a topographical support member and a method for forming a topographical support member for producing nonwoven fabrics having raised portions. The support members of the present invention comprise a body portion having a top surface including a first micro-sized topographical pattern and a plurality of apertures through its thickness. The body portion further comprises at least one macro-sized region disposed below said top surface. The micro-sized pattern produces the background portion of the nonwoven fabric. The macro-sized region produces raised portions of the fabric conforming to the shape and depth of the macro-sized region. The macro-sized recessed region preferably has the same topographical pattern as the top surface of the support member, however, the regions may have a different pattern or no pattern. In addition, the macro-sized region may include a major surface recessed a first depth below the top surface and one or more minor surfaces recessed at depths different from the first depth. For example, one minor surface surrounding the major surface may be provided that is recessed at a depth below the first depth and has a diameter or a cross-sectional width substantially less than the width of the major surface.
The topographical pattern comprising the top surface of the support member is preferably produced by a laser drilling process. The laser drilling process produces a plurality of peaks, valleys and apertures in the top surface of the support members. The macro-sized regions, formed by a laser ablation process, have a cross-sectional width larger than the repeat spacing of the repeating pattern.